Extend DLTK preferences by adding library version
[414776] Severe performance Thread.sleep() bottleneck in JobManager

Avoid sleeping 50 ms after each processed file

Bug: https://bugs.eclipse.org/bugs/show_bug.cgi?id=414776
Signed-off-by: Kaloyan Raev <kaloyan.r@zend.com>
[415137] h2 model db should be indexed

Add index for the (PATH, CONTAINER_ID) columns of the FILE table. This
improves significantly the performance of executing select/update/delete
statements on the h2 db when it grows with many file records.

Other columns used in prepared statements are indexed automatically by
the h2 db and it is not necessary to explicitly create indices for them:
  - CONTAINERS > PATH - because it is UNIQUE
  - FILES > CONTAINER_ID - because it is a foreign key

Bug: https://bugs.eclipse.org/bugs/show_bug.cgi?id=415137
Signed-off-by: Kaloyan Raev <kaloyan.r@zend.com>
[414937] Source modules are indexed twice

Remove processing of SCRIPT_FOLDER units. Any folder's children will be
anyway processed as SCRIPT_MODULE units.

Bug: https://bugs.eclipse.org/bugs/show_bug.cgi?id=414937
Signed-off-by: Kaloyan Raev <kaloyan.r@zend.com>